The term "high frequency" used in the present application generally refers to 1 MHz or higher frequencies. The thin film magnetic head is one employed most advantageously with a magnetic disk or a magnetic tape in cases where the magnetic recording density and the working frequency of the magnetic recording medium are extremely high. An induction type thin layer magnetic head, which relies upon electro-magnetic induction, is comprised of a lower magnetic pole film and an upper magnetic pole film making up a magnetic circuit having a magnetic gap, a coil conductor film interlinked with this magnetic circuit, and an insulation film, adapted for electrically and magnetically insulating magnetic coils from one another or from the magnetic poles, these various films being formed by thin film forming and precision processing techniques and laminated one upon the other to form a thin magnetic film.
Such induction type thin film magnetic head usually employs fine-structured magnetic cores (microcores) formed by thin films of soft magnetic metal, and hence is subject to lesser core losses at high frequencies, such as eddy current losses, than the bulk type magnetic head. In addition, the magnetic circuit may be compact in size. Thus, with the use of the induction type thin film magnetic head, recording and reproducing efficiencies may be improved in magnetic recording and reproduction over a broader range of frequencies. The induction type thin film magnetic head is also essentially suitable for use in high frequency high density magnetic recording since it may be formed by a microcore and coil winding (microcoil) and hence may be of lower impedance.
The electro-magnetic conversion characteristics of such thin film magnetic head greatly depend on the magnetic properties of the magnetic pole films. That is, for achieving sufficient recording on a high coercivity magnetic medium which enables recording at shorter wavelengths, the magnetic pole films having a high saturation flux density are required. On the other hand, for achieving faithful and efficient recording and/or reproduction of high frequency signals, high magnetic permeability in the high frequency range is required.
Generally for achieving high magnetic permeability, it is necessary to adopt rotation of magnetization with a high switching speed, rather than the magnetic wall movement, as the magnetization process. To this end, it is necessary for the magnetic pole films to be provided with uniaxial magnetic anisotropy so that the direction of the track width of the thin film magnetic head represents the axis of easy magnetization, and for the axis of difficult magnetization to coincide with the direction of magnetic excitation.